kvutils: Simplify calculating the weight of a Caffeine cache. (#5461)

* kvutils: Simplify calculating the weight of a Caffeine cache.

And remove an errant `println` that slipped through the cracks.

Thank you to @ben-manes for the tip!

CHANGELOG_BEGIN
CHANGELOG_END

* kvutils: Make classes final and defs into vals.

Co-Authored-By: Stefano Baghino <stefano.baghino@digitalasset.com>

Co-authored-by: Stefano Baghino <stefano.baghino@digitalasset.com>

ledger/participant-state/kvutils/src/main/scala/com/daml/ledger/participant/state/kvutils/caching/Cache.scala

@@ -5,14 +5,14 @@ package com.daml.ledger.participant.state.kvutils.caching
 
 import com.github.benmanes.caffeine.{cache => caffeine}
 
-import scala.collection.JavaConverters._
+import scala.compat.java8.OptionConverters._
 
 trait Cache[Key, Value] {
   def get(key: Key, acquire: Key => Value): Value
 
   def size: Size
 
-  private[caching] def entries: Iterable[(Key, Value)]
+  def weight: Size
 }
 
 object Cache {
@@ -29,26 +29,28 @@ object Cache {
           caffeine.Caffeine
             .newBuilder()
             .maximumWeight(maximumWeight)
-            .weigher[Key, Value](Weight.weigher)
+            .weigher(Weight.weigher[Key, Value])
             .build[Key, Value]())
     }
 
-  class NoCache[Key, Value] extends Cache[Key, Value] {
+  final class NoCache[Key, Value] extends Cache[Key, Value] {
     override def get(key: Key, acquire: Key => Value): Value = acquire(key)
 
-    override def size: Size = 0
+    override val size: Size = 0
 
-    override private[caching] def entries: Iterable[(Key, Value)] = Iterable.empty
+    override val weight: Size = 0
   }
 
-  class CaffeineCache[Key, Value](val cache: caffeine.Cache[Key, Value]) extends Cache[Key, Value] {
+  final class CaffeineCache[Key, Value](val cache: caffeine.Cache[Key, Value])
+      extends Cache[Key, Value] {
     override def get(key: Key, acquire: Key => Value): Value =
       cache.get(key, key => acquire(key))
 
     override def size: Size =
       cache.estimatedSize()
 
-    override private[caching] def entries: Iterable[(Key, Value)] =
-      cache.asMap().asScala
+    override def weight: Size =
+      cache.policy().eviction().asScala.flatMap(_.weightedSize().asScala).getOrElse(0)
   }
+
 }

ledger/participant-state/kvutils/src/main/scala/com/daml/ledger/participant/state/kvutils/caching/Weight.scala

@@ -21,12 +21,6 @@ object Weight {
   def weigher[Key: Weight, Value: Weight]: caffeine.Weigher[Key, Value] =
     new WeightWeigher[Key, Value]
 
-  def ofCache[Key, Value](cache: Cache[Key, Value])(
-      implicit keyWeight: Weight[Key],
-      valueWeight: Weight[Value],
-  ): Size =
-    cache.entries.map { case (key, value) => keyWeight.weigh(key) + valueWeight.weigh(value) }.sum
-
   implicit object `Bytes Weight` extends Weight[Bytes] {
     override def weigh(value: Bytes): Size =
       value.size().toLong

ledger/participant-state/kvutils/src/main/scala/com/daml/ledger/validator/SubmissionValidator.scala

@@ -10,7 +10,7 @@ import com.codahale.metrics.{MetricRegistry, Timer}
 import com.daml.ledger.participant.state.kvutils
 import com.daml.ledger.participant.state.kvutils.DamlKvutils._
 import com.daml.ledger.participant.state.kvutils.api.LedgerReader
-import com.daml.ledger.participant.state.kvutils.caching.{Cache, Weight}
+import com.daml.ledger.participant.state.kvutils.caching.Cache
 import com.daml.ledger.participant.state.kvutils.{Bytes, Envelope, KeyValueCommitting}
 import com.daml.ledger.participant.state.metrics.MetricName
 import com.daml.ledger.participant.state.metrics.Metrics.timedFuture
@@ -302,16 +302,8 @@ class SubmissionValidator[LogResult] private[validator] (
     val transformSubmission: Timer = metricRegistry.timer(prefix :+ "transform_submission")
 
     private val stateValueCachePrefix: MetricName = prefix :+ "state_value_cache"
-    metricRegistry.gauge(
-      stateValueCachePrefix :+ "size",
-      () =>
-        () => {
-          println(s"State value cache size = ${stateValueCache.size}")
-          stateValueCache.size
-      })
-    metricRegistry.gauge(
-      stateValueCachePrefix :+ "weight",
-      () => () => Weight.ofCache(stateValueCache))
+    metricRegistry.gauge(stateValueCachePrefix :+ "size", () => () => stateValueCache.size)
+    metricRegistry.gauge(stateValueCachePrefix :+ "weight", () => () => stateValueCache.weight)
   }
 }